Nitride semiconductor device and fabrication method therefor

Abstract

A nitride semiconductor device includes an electron transit layer ( 103 ) that is formed of a nitride semiconductor, an electron supply layer ( 104 ) that is formed on the electron transit layer ( 103 ), that is formed of a nitride semiconductor whose composition is different from the electron transit layer ( 103 ) and that has a recess ( 109 ) which reaches the electron transit layer ( 103 ) from a surface, a thermal oxide film ( 111 ) that is formed on the surface of the electron transit layer ( 103 ) exposed within the recess ( 109 ), a gate insulating film ( 110 ) that is embedded within the recess ( 109 ) so as to be in contact with the thermal oxide film ( 111 ), a gate electrode ( 108 ) that is formed on the gate insulating film ( 110 ) and that is opposite to the electron transit layer ( 103 ) across the thermal oxide film ( 111 ) and the gate insulating film ( 110 ), and a source electrode ( 106 ) and a drain electrode ( 107 ) that are provided on the electron supply layer ( 104 ) at an interval such that the gate electrode ( 108 ) intervenes therebetween.

What is claimed is: 
     
       1. A nitride semiconductor device comprising:
 a substrate; 
 an electron transit layer that is formed on the substrate, and that is formed of a nitride semiconductor; 
 an electron supply layer that is formed on the electron transit layer, and that is formed of a nitride semiconductor whose composition is different from the electron transit layer; 
 an AlGaN buffer layer that intervenes between the substrate and the electron transit layer, and that includes a high aluminum composition region whose aluminum composition is relatively high and a low aluminum composition region whose aluminum composition is lower than the high aluminum composition region and which is arranged in a region close to the electron transit layer as compared with the high aluminum composition region; and 
 an element separation layer that is formed with a region whose resistance is increased by causing a crystal defect through ion implantation, and that passes through the electron supply layer, the electron transit layer, and the low aluminum composition region to reach the high aluminum composition region, a bottom portion of the element separation layer being located within the high aluminum composition region. 
 
     
     
       2. The nitride semiconductor device according to  claim 1 ,
 wherein the AlGaN buffer layer is an AlGaN layer whose aluminum composition is adjusted such that as the AlGaN buffer layer approaches the electron transit layer in a direction of a layer thickness from the substrate toward the electron transit layer, the aluminum composition is decreased. 
 
     
     
       3. The nitride semiconductor device according to  claim 1 ,
 wherein the AlGaN buffer layer includes a first aluminum composition AlGaN layer that has a first aluminum composition and a second aluminum composition AlGaN layer that is deposited on a side of the electron transit layer with respect to the first aluminum composition AlGaN layer and that has a second aluminum composition lower than the first aluminum composition, and 
 the high aluminum composition region includes the first aluminum composition AlGaN layer, and the low aluminum composition region includes the second aluminum composition AlGaN layer. 
 
     
     
       4. The nitride semiconductor device according to  claim 1 , further comprising:
 an AlN buffer layer that intervenes between the AlGaN buffer layer and the substrate. 
 
     
     
       5. The nitride semiconductor device according to  claim 1 ,
 wherein the element separation layer is formed so as to surround an element region. 
 
     
     
       6. The nitride semiconductor device according to  claim 1 , further comprising:
 a wiring that is arranged on the element separation layer. 
 
     
     
       7. The nitride semiconductor device according to  claim 1 ,
 wherein the element separation layer is formed so as to separate a plurality of element regions, and 
 the nitride semiconductor device further comprises an element-to-element wiring that connects between a plurality of elements respectively formed in the element regions. 
 
     
     
       8. The nitride semiconductor device according to  claim 7 ,
 wherein the elements respectively formed in the element regions include two or more elements having different functions. 
 
     
     
       9. The nitride semiconductor device according to  claim 7 ,
 wherein the elements respectively formed in the element regions include two or more elements having a common function. 
 
     
     
       10. The nitride semiconductor device according to  claim 7 ,
 wherein the element separation layer is formed so as to surround the element regions of the elements connected with the element-to-element wiring. 
 
     
     
       11. The nitride semiconductor device according to  claim 1 ,
 wherein the element separation layer is a high resistance layer that is formed by ion implantation using, as a material, an element whose mass number is less than 10 but more than 2. 
 
     
     
       12. The nitride semiconductor device according to  claim 1 ,
 wherein the element separation layer is a high resistance layer that is formed by implantation of a helium ion. 
 
     
     
       13. The nitride semiconductor device according to  claim 1 ,
 wherein the element separation layer is a high resistance layer that is formed by ion implantation using a plurality of acceleration energies. 
 
     
     
       14. The nitride semiconductor device according to  claim 1 ,
 wherein the element separation layer is a high resistance layer that is formed by ion implantation from a direction inclined with respect to a direction of thickness of the electron transit layer. 
 
     
     
       15. The nitride semiconductor device according to  claim 14 ,
 wherein an inclination angle of the ion implantation direction with respect to the direction of the thickness of the electron transit layer is 5 to 10 degrees. 
 
     
     
       16. The nitride semiconductor device according to  claim 1 ,
 wherein the electron transit layer is formed of GaN, and the electron supply layer is formed of AlGaN. 
 
     
     
       17. The nitride semiconductor device according to  claim 1 ,
 wherein the electron transit layer is a GaN layer having a thickness of 400 nm or more. 
 
     
     
       18. The nitride semiconductor device according to  claim 1 , further comprising:
 a source electrode and a drain electrode that are arranged at an interval on the electron supply layer; and 
 a gate electrode that is arranged opposite to the electron transit layer between the source electrode and the drain electrode. 
 
     
     
       19. The nitride semiconductor device according to  claim 18 ,
 wherein the gate electrode is formed so as to surround the source electrode together with the element separation layer. 
 
     
     
       20. The nitride semiconductor device according to  claim 18 , further comprising:
 an interlayer insulating film that covers the source electrode, the drain electrode and the gate electrode; 
 a source wiring film that is connected to the source electrode via a source contact hole passing through the interlayer insulating film and that is arranged on the interlayer insulating film; and 
 a drain wiring film that is connected to the drain electrode via a drain contact hole passing through the interlayer insulating film and that is arranged on the interlayer insulating film, 
 wherein the source wiring film and the drain wiring film are formed in such a pattern that on the interlayer insulating film, the source wiring film and the drain wiring film mesh with each other in a comb tooth shape. 
 
     
     
       21. The nitride semiconductor device according to  claim 18 , which is the nitride semiconductor device further comprising a wiring that is arranged on the element separation layer,
 wherein the wiring includes a gate wiring connected to the gate electrode. 
 
     
     
       22. A method of manufacturing a nitride semiconductor device, the method comprising:
 a step of forming an AlGaN buffer layer by epitaxially growing an AlGaN crystal on a substrate such that an aluminum composition is relatively high in a high aluminum composition region close to the substrate and the aluminum composition is relatively low in a low aluminum composition region away from the substrate; 
 a step of forming an electron transit layer by epitaxially growing a nitride semiconductor on the AlGaN buffer layer; 
 a step of forming an electron supply layer on the electron transit layer by epitaxially growing a nitride semiconductor layer whose composition is different from the electron transit layer; and 
 a step of forming a high resistance element separation layer that passes through the electron supply layer, the electron transit layer, and the low aluminum composition region to reach the high aluminum composition region by breaking a crystal structure through ion implantation on the electron supply layer, the electron transit layer, and the high aluminum composition region, wherein a bottom portion of the high resistance element separation layer is located within the high aluminum composition region. 
 
     
     
       23. The method of manufacturing a nitride semiconductor device according to  claim 22 ,
 wherein the step of forming the AlGaN buffer layer includes a step of forming a first aluminum composition AlGaN layer of a first aluminum composition and a step of forming, in a higher position than a position of the first aluminum composition AlGaN layer, a second aluminum composition AlGaN layer of a second aluminum composition lower than the first aluminum composition. 
 
     
     
       24. The method of manufacturing a nitride semiconductor device according to  claim 22 , the method further comprising:
 a step of forming an AlN buffer layer on the substrate before the step of forming the AlGaN buffer layer such that the AlGaN buffer layer is formed on the AlN buffer layer. 
 
     
     
       25. The method of manufacturing a nitride semiconductor device according to  claim 22 ,
 wherein the element separation layer is formed so as to surround an element region. 
 
     
     
       26. The method of manufacturing a nitride semiconductor device according to  claim 22 ,
 wherein the element separation layer is formed so as to separate a plurality of element regions, and 
 the method of manufacturing a nitride semiconductor device further comprises a step of forming an element-to-element wiring that connects between elements respectively formed in the element regions. 
 
     
     
       27. The method of manufacturing a nitride semiconductor device according to  claim 22 ,
 wherein the ion implantation is performed using, as a material, an element whose mass number is less than 10 but more than 2. 
 
     
     
       28. The method of manufacturing a nitride semiconductor device according to  claim 22 ,
 wherein the ion implantation is performed using helium ions. 
 
     
     
       29. The method of manufacturing a nitride semiconductor device according to  claim 22 ,
 wherein the ion implantation is performed using a plurality of acceleration energies. 
 
     
     
       30. The method of manufacturing a nitride semiconductor device according to  claim 22 ,
 wherein the ion implantation is performed from a direction inclined with respect to a major surface of the substrate. 
 
     
     
       31. The method of manufacturing a nitride semiconductor device according to  claim 30 ,
 wherein the ion implantation is performed from a direction inclined at an angle of 5 to 10 degrees with respect to a normal direction to the major surface of the substrate. 
 
     
     
       32. The method of manufacturing a nitride semiconductor device according to  claim 22 ,
 wherein the step of forming the electron transit layer includes a step of epitaxially growing a GaN layer having a thickness of 400 nm or more.